Do you feel the nip in the air? Runners do. For them, the advent of fall means more than changing leaves and back to school. Cooler weather and coming races make autumn the ideal time to run in the great outdoors. For some runners, nothing beats the off-road experience. Here are 12 great trails endorsed by the enthusiastic members of local running clubs. • Read more about the trails: Runners' top 12 Baltimore-area trails